Impedance modelling on multiple dielectric builds

As printed circuit board (PCB) track geometries shrink, sometimes it becomes necessary to look deeper than the material data sheet when modelling electrical properties of transmission lines; this study looks at how variation in dielectric constant should be handled in multiple and single dielectric PCB builds. This paper describes how even FR4 builds should in some cases be treated as multiple dielectric builds. Approaches for understanding the root cause of effective dielectric constant variation with structure, coupling and scale are considered. An outline of the implementation of the boundary element method is provided for those wishing to look a little deeper into the modelling process. Finally, a brief investigation covers the sources of measurement errors aimed at helping to put the best data back into the modelling process.